Drawing Penrose diagram figures

I need to create a figure of a Penrose diagram and I wonder if there is a dedicated program to this task. I know it's only a bunch of nested squares and lines but some people like me are simply uncapable of drawing anything by hand!

This probably isn't helpful for you, but I parameterized the u = const and v = const lines (well, their conformal equivalents) and plotted them using mathematica. Then I plotted a square around them =).